[illumos-Developer] Ugh... xdr_{float,double} problems

[Garrett D'Amore]

If that particular pragma is so widely used, then lets just go ahead and
keep it for now.

	- Garrett

On Sun, 2011-01-30 at 15:33 -0600, Jason King wrote:
> On Sun, Jan 30, 2011 at 2:52 PM, Garrett D'Amore <garrett at nexenta.com> wrote:
> > General review feedback:
> >
> > No spacing between # and CPP directives, please.
> 
> Fixed.
> 
> >
> > I'm a bit worried about pragma redefine_extname -- what happens to that
> > on gcc or Studio?  Do they both support it?
> 
> They should -- it's used extensively throughout the code already
> (stdio, sockets, etc. about 150 times), studio definitely does, if gcc
> doesn't there would be much bigger problems :)
> 
> >
> > I'm thinking #error might be better here.... it would force people
> > working on alternate processor ports to adapt the code...
> 
> In that case, should we just ditch the portable implementation altogether?
> 
> >
> >        - Garrett
> >
> > On Sun, 2011-01-30 at 14:27 -0600, Jason King wrote:
> >> Yeah, basically I'm a dumbass and shouldn't try to bugfix during weeks
> >> where I'm sleep deprived (my apologies to everyone for that).  Dr.
> >> Grabowski was right
> >>
> >> I see the problem, and was able to get access to a S10 (sparc & x86)
> >> box to obtain a known good XDR bytestream (of floats and doubles) to
> >> test against so the test can be more definitive.
> >>
> >> I have a webrev of the fix here: http://cr.illumos.org/view/kc6gu36g/
> >> The #pragma redefine_extname bit was a suggestion from Gordon (just to
> >> help people porting to other platforms out).
> >>
> >> I really need to run errands now but will be back later to post the
> >> test code (short version, I take the known good stream from s10
> >> x86/sparc, decode it, compare values, then encode the values to
> >> another stream and compare vs. trying to 'guess' the correct values in
> >> the previous test), and take care of the rest.
> >>
> >> On Sat, Jan 29, 2011 at 10:05 PM, Garrett D'Amore <garrett at nexenta.com> wrote:
> >> > Any update on this?  I've not had a chance yet to backout your change..
> >> > I'm not sure what the right thing to do here is... I'd rather have a
> >> > "real" fix.
> >> >
> >> >        - Garrett
> >> >
> >> > On Fri, 2011-01-28 at 12:10 -0600, Jason King wrote:
> >> >> Ok, however things will still be broken, my fix just breaks (or more
> >> >> precisely, breaks everyone's workarounds) faster.  I can probably have
> >> >> a true fix later tonight as well.
> >> >>
> >> >> On Fri, Jan 28, 2011 at 10:58 AM, Garrett D'Amore <garrett at nexenta.com> wrote:
> >> >> > Ok, I'll backout the changes.  Can you please file a bug?  I probably won't
> >> >> > get around to backing this change out until tonight as I'm traveling and on
> >> >> > limited battery power.
> >> >> >
> >> >> >    - Garrett
> >> >> >
> >> >> > On 01/28/11 08:48 AM, Jason King wrote:
> >> >> >>
> >> >> >> After lengthy discussions, and even more digging... it looks like
> >> >> >> there's a bit of a very-long standing mess with the C xdr API.
> >> >> >>
> >> >> >> The problem is, the OTW XDR format for 32&  64 bit doubles is
> >> >> >> identical on x86, amd64, sparc, and sparcv9.  In theory, the code
> >> >> >> should then just merely copy the values out unchanged.
> >> >> >> However, that really happened was on little-endian platforms, the byte
> >> >> >> values for fp values were being (incorrectly) byteswapped by the
> >> >> >> library.  Instead of fixing the library, it appears the existing
> >> >> >> software that actually uses fp with xdr workaround the bug on those
> >> >> >> platforms.  Of course the recent putback broke the workaround.
> >> >> >>
> >> >> >> Essentially:
> >> >> >>
> >> >> >> 1. code is released with broken xdr_{float,double}
> >> >> >> 2. code is written w/ workarounds
> >> >> >> 3. code is updated, and __amd64 define is (incorrectly) changed to
> >> >> >> amd64.  This causes xdr_{float,double} to revert to a slower, platform
> >> >> >> independent version that correctly (minus rouding errors) writes the
> >> >> >> value into the stream (without swapping).
> >> >> >> 4. My fix correctly writes fp values unchanged to XDR stream, but also
> >> >> >> breaks any software with workarounds.  The test cases were written to
> >> >> >> the RFC&  man pages (since I couldn't really find anything out there
> >> >> >> that uses
> >> >> >>
> >> >> >> Given the pervasiveness of this, we probably need to do something similar
> >> >> >> to:
> >> >> >>
> >> >> >> 1. Revert the behavior to the traditional broken behavior
> >> >> >> 2. Update the man pages to document this behavior
> >> >> >> 3. Add a #define to the rpc/xdr.h header file (XDR_FLOAT_NO_SWAP ?) to
> >> >> >> allow applications to select the correct behavior when defined (and
> >> >> >> document this in the manpage).
> >> >> >>
> >> >> >> _______________________________________________
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> >> >> >> Developer at lists.illumos.org
> >> >> >> http://lists.illumos.org/m/listinfo/developer
> >> >> >>
> >> >> >
> >> >> >
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